Make sure you are unblocking the setup file. Right click it, go to properties, click unblock.
Try postgres 8.3
1) Click start - accessories
2) Right click command prompt
3) Choose Run as Administrator
Type:
sfc /scannow
Hit enter
4) Please schedule a disk check:
chkdsk /f /r C:
5) Hit enter
6) Restart your computer.
Afterwards, it will either show there are no integrity problems, or give a location for a file with errors. If this happens, please send us that file.